An experiment at the Max Planck Institute, Berlin, in 2008 showed that when you decide to move your hand, the decision can be seen in your brain, with an MRI scanner, before you are aware you have made a decision. The delay is around six seconds. During that time, your mind is made up but your consciousness doesn’t acknowledge the decision until your hand moves.

One interpretation of this is that your consciousness – the thing you think of as ‘you’ – is just a passenger inside a deterministic automaton. Your unconscious brain and your body get on with running your life, and only report back to your conscious mind when necessary to preserve a sense of free will. But it’s just as valid to say that when you make a decision, there’s always a certain amount of background processing going on, which the conscious mind ignores for convenience. In the same way, your eye projects an upside-down image onto your retina, but your unconscious brain turns it the right way around.